Heat exchanger



Nov. 14, 1950 E. e. SCHEIBEL 2,529,516

HEAT EXCHANGEK Filed Jan. 15, 1946 2 Sheets-Sheet l INVENTOR EDWARD ascnnsu.

L2 WW ATTORNEY Nov. 14, 1950 E. G. SCHEIBEL 2,529,515

HEAT EXCHANGER Filed Jan. 15, 1946 2 Sheets-Sheet 2 INVENTOR EDWARD ascnmbu WW 41M ATTORNEY Patented Nov. 14, 1950 2,529,516 HEAT EXCHANGER Edward G. Scheibel, Nutley, N. J., minor to Hydrocarbon Research, Inc., New York, N. Y.

Application January 15, 1946, Serial No. 641,276 9 Claims. (Cl. 257-224) The present invention relates to an improved exchanger for recovering the cold content of the outgoing oxygen and nitrogen products of rectifications, which may be at a temperature of about 280 F., in the production of oxygen by the liquefaction and rectification of air.

Cold accumulators or regenerators (hereinafter referred to as cold exchangers) of large cold-absorbing capacity are well known. In these cold exchangers, the relatively warm incoming air and the relatively cold outgoing oxygen d nitrogen products of rectification are alternately passed with periodically reversed operation, so that streams of warm air are fiowed through the same packing-filled spaces as the cold oxygen and nitrogen traversed during the preceding step in the process, the high-boiling impurities deposited in these spaces during the passage of the air therethrough being removed by sublimation during the subsequent flow therethrough of the products of rectification.

In the design of such exchangers, various confiicting factors must be compensated for in order to obtain reasonably satisfactory operation. Thus, for example, the cold exchangers must provide for high cold transfer efficiency and high throughputs and yet the volumetric space through which the fluids flow must be relatively small in order to minimize power loss since, upon each reversal, the volume of compressed air in the cold exchangers is lost and must be again replaced, and also in order to avoid undue dilution of (a) the compressed air stream flowing to the rectification system with nitrogen, and (b) the nitrogen stream with air, which dilution necessarily takes place upon each reversal of fiow, causing the air stream to flow through the packing-filled spaces containing nitrogen, and the nitrogen stream to fiow through the packing-filled spaces containing air, left therein from the streams of nitrogen and air, respectively, passed therethrough during the preceding steps of the process.

Among the objects of this invention are to provide a heat exchanger which has a relatively small over-all volume, thereby minimizing reversal losses; which has an exceptionally high surface area of cold exchanger surface per unit of volume and which is otherwise designedso that it is of high cold transfer efficiency; which is of high throughput capacity; which is relatively easy to fabricate; which provides for flow of oxygen, nitrogen and air in cold exchange relationship and for the periodic reversal of the nitrogen and air streams to effect removal by sublimation of any condensible matter removed from the air stream during the preceding step of the process; which, notwithstanding the parts, are composed of different metals, having different coeificients of expansion, in the interests of economy and efiiciency of cold transfer, is designed to accommodate expansion and contraction of the parts due to temperature changes; and in the operation of which minimum of fluids flowing therethrough tales place.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In the accompanying drawings forming a part a of this specification and showing for purposes of exemplification a preferred form of this invention without limiting the claimed invention to such illustrative instance:

Figure 1 is a composite view of a cold exchanger embodyin this invention, the lower half being a vertical section through the exchanger, and the upper half a side elevation;

Figure 2 is a right side elevational view of the upper portion of the apparatus of Figure 1;

Figure 3 is a diagrammatic sectional plan view taken between baffles 36 and 36 of Figure 1, showing the arrangement of the tubes in a bundle, which bundle of tubes is inserted in a shell such as shown in Figures 1 and 2;

Figure 4 is a sectional view of one of the cold exchanger tubes taken normal to the length of the tube to show the construction and arrangement of the interior and exterior fins; and

Figure 5 is a vertical section through part of one of the oxygen tubes, showing the expansion bellows therein and the connection in the tube between the header plates through which it extends.

Referring to Figure 1 of the drawings, reference numeral it indicates a cylindrical. shell which may be of nickel steel containing approximately 8% nickel or of other suitable metal. The shell is preferably in the form of a cylinder or drum, having concavo-convex ends ll provided with centrally disposed openings l2 for the inlet to and exit from the shell ill of oxygen flowing from a rectification system of an oxygen plant. Intermediate the ends of the shell I II are a series of raised and depressed portions or corrugations l3 extending completely around the shell l0 and forming an expansion joint. This expansion joint accommodates differential expansion and contraction of the intermediate portion of the shell, 1. e., the portion between the inner header plates l4, hereinafter described,

pressure drop and the cold exchanger tubes in this intermediate portion of the shell which, as more fully described hereinafter, are made of a metal, such as copper, of high thermal conductivity capacity and of diilerent coeillcient of expansion than the metal of shell l0. Supporting members or brackets (not shown) may be welded or otherwise fastened to the outside of the shell l0, adapted to rest on suitable blocks or other supports for maintaining the shell, preferably, in a horizontal posi tion.

At each end of the shell, a concavo-convex header plate l5, desirably concentric with the ends ll of the shell, has the marginal portion 16 welded or otherwise secured, to form a gas-tight seal with the interior wall of the shell l0. Preferably, the marginal portion of the header plates IS in contact with the interior walls of the shell I0, is of substantial area in a longitudinal direction relative to the longitudinal axis of the shell to insure the maintenance of a gas-tight seal. Thus an oxygen header I1 is formed at each end of the shell. The aforementioned inner header plates H are spaced from the header plates in a longitudinal direction a minimum distance to provide inner headers l8 adjacent the headers H, which headers I8 are of sufiicient capacity to accommodate the air or nitrogen flowing there- 'through during alternate periods of operation.

The header plates M are preferably in the form of flat plates, the edges of which are welded or otherwise suitably secured to the interior side wall of the shell l0. Each of the headers l8 are provided with ports I9. From Figs. 1 and 2 it is evident that each port I! has a dimension along the length of the shell substantially equal to the space between the end of header plate I5 and the header plate l4 and has a dimension in a direction along the circumference of the shell greater than (e. g., about double) that in the longitudinal direction of the shell. In other words, the ports are of substantially elliptical shape.

Each port l9 communicates with a flared conduit or transitional piece to accommodate the substantially elliptical shape of the port, the flared conduit 20 terminating in a circular opening 2! which may be suitably joined to usual piping for flowing air therethrough or nitrogen during alternate steps of the process. Thus largesize pipes may be connected to the shell through transitional ports without necessitating an increase in the length of the shell, which increase in length of the shell would necessarily result in an increase in the length of the cold exchanger tubes, hereinafter described, with consequently increased cost of the cold exchanger.

Each of the inner headers II is provided with a suitable manhole 22 to permit a mechanic to make the connections in the exchanger tubes, hereinafter described, between the header plates l4 and I5, or for other purposes. Cover-plates (not shown) are used to seal these manholes when the cold exchanger is in operation.

The intermediate portion 23 of the shell, i. e., the portion between the header plates I4, is provided at each end with a port 24 and associated flared piece 25 terminating with circular opening 26, which are of a construction similar to the construction of ports l9 and flared pieces 20 with openings 2| hereinabove described. While 7 in the drawing one port is shown for each header l8 and one at each end of the intermediate portion 23, it will be understood any desired number of such ports may be employed, particularly in cold exchangers of large diameter to ensure uniform gas flows throughout the cross-section of the exchanger.

It should be noted ports 24, like ports l9, have a smaller dimension along lines parallel to the longitudinal axis of the shell, and a larger dimension along the circumference of the shell, thus providing for maximum port opening to the intermediate portion 23 with minimum utilization of the length of the shell, and consequent economy in exchanger construction. Disposed within the shell l0 are two sets of exchanger tubes. One set consists of tubes 21 extending between header plates l5 connecting the end headers l1 and are used for flow of oxygen therethrough. These tubes are disposed in spaced relationship, and as shown in Fig. 5 have their ends rolled into grooves 28 within header plates 15, thus making gas-tight joints with 'these header plates. The portions of the oxygen tubes passing through header plates M, as shown in Fig. 5, are similarly rolled into grooves 29 in the header plates l4, and thus a gas-tight seal is formed preventing leakage from one side of the header plates H to the other. Other suitable gas-tight connections than those hereinabove described between the tubes and the header plates could be employed, if desired.

As shown in Fig. 1 and in greater detail in Fig. 5, each oxygen tube 21 is preferably made in three sections, one relatively long middle section 21a passing through header plates l4 and two relatively short end sections 21b passing through header plates IS. The middle section 21a is joined to end section 21b by sleeves 30. The end sections 21b have a corrugated or bellows portion 3| to permit expansion and contraction of the oxygen tubes 2'! between header plates H and I5. Two such expansion bellows are provided in each oxygen tube, one positioned at each end of shell ID. The oxygen tubes, as well as the other set of tubes, hereinafter described, and the header plates, are preferably made of electrolytic copper which is of high heat; transfer efllciency or other metal, such as aluminum or alloys of high heat transfer capacity.

Since the oxygen tubes 21 are of different metal than the shell, they have a different coefficient of expansion. The expansion bellows 3|, hereinabove described, minimize formation of stresses due to differential expansion or contraction of the oxygen tubes on the one hand, and the shell on the other. By forming the oxygen tubes with the expansion bellows 3|, the necessity for providing expansion joints in the portions of the shell between the header plates l4 and I5 is eliminated, with consequent saving in the length of the shell and greatly decreasing the cost of the cold exchanger. It will be noted there is a relatively small number of oxygen tubes in the exchanger, so that the work involved in providing expansion bellows therein is not excessive. Differential expansion and contraction taking place in the intermediate portion 23 of the shell,- through which portion all tubes pass, is taken care of by the expansion joint i3.

Referring to Fig. l, the second set of tubes, one of which is indicated by reference character 32, extends between. the header plates H. The ends of these tubes may be connected to the header plates l4, so they make a gas-tight seal with the openings therein, in the same manner as the oxygen tubes 21 are connected with the header plates I4 as hereinabove described. Thus the headers ill at opposite ends of the shell are communicably connected through the tubes 32.

Desirably, the number oftubes 32 are four times the number of oxygen tubes 21, the exchanger containing not less than or tubes, the exact number depending upon the volume of oxygen, nitrogen and air to be handled. The tubes are preferably cylindrical; however, a

hexagonal tube or even a square tube may be used if desired.

Each tube of both sets of tubes-is provided with an interior fin 33, Fig. 4, and an exterior fln 34, the fins being of a metal of high thermal conductivity, the same as that of the tubes and of foillike thickness, for example, from .005 to .020" in thickness, preferably a thickness of .008 to .010". The interior fin 33 is constructed and arranged to provide a multiplicity of interrupted contiguous channels extending longitudinally through the tube. In the preferred embodiment shown in the drawings, the interior fin for each section of tube length is produced by folding two strips of foillike copper to form four sets of substantially isosceles triangles, two sets filling one half of the tube and the other two sets the other half. One set of triangles 33a have their base portions in flat contact with the interior wall of the tube 21 or 32. The other set of triangles 33?) have their base portions disposed remote from the interior wall of the tube in a plane bisecting the tube longitudinally. The other two sets of triangles 33c and 33d are disposed in like manner in the other half of the tube, the bases, of the triangles 330 being in fiat contact with the interior wall of the tube and the bases of the triangles 33d being in contact with the bases of the triangles 331).

like to form four sets of triangles, as hereinabove described, results in the fins maintaining the position shown in Fig. 4 to form the longitudinally extending channels; if only one strip were used and folded in accordion fashion to form longitudinal channels on the inside of the tube, some of the fins would have a tendency to collapse and touch each other, particularly in the case of larger tubes because of the length of the sidewalls of the triangular channels. This would be wasteful of heat exchanger surface. The fins are desirably bonded to the interior and exterior of each tube by coating the interior and exterior walls of the tube with solder metal, placing the fins, folded as shown in Fig. 4, in contact with the solder coating, then placing the assembly in an oven and heating it to a temperature so that the solder on the tube walls wets the fins, and later cooling, thereby obtaining a firm bond between the tube walls and the portions of the fins in flat contact with the tube walls.

The exterior fin 34 is folded to provide two sets of contiguous triangles 34a. and 34b, the bases of the triangles 34a being in flat contact with the exterior of the tube and the bases of the triangles 34b being remote from the wall of the tube and forming a hexagonal outline as clearly shown in Fig. 4. Instead of the hexagonal outline of Fig. 4, the triangles may be arranged to produce a substantially square or other polygonal outline; the hexagonal outline is preferred. While Fig. 4 shows the interior fin 33 as made from two pieces of folded foil-like metal and the exterior fin 34 as made from one piece, it is obvious that both might be formed from a difierent number of pieces, e. g., four pieces for the interior fin 33 and six pieces (one for each side of the hexagonal outline) for the exterior fin 34. v

It is important that the exterior fin 34 have an accurately dimensioned outline so that a multi- 6 'plicity ofv tubes can be nested together withgood metal-to-metal contact between the exterior fins of adjacent tubes. A convenient method of en suring that the dimensions of the outline of the exterior fin 34 are held to close tolerances is to draw each tube with the exterior fin 34 bonded thereto through a suitable die before assembling the tubes in a nested tube bundle.

The accordion-like fins on the interior and exterior of the tubes are formed by folding strips of foil-like copper from 4 to 12" wide, preferably about 8" wide. The triangular channels provided by these fin sections are therefore 4 to 12" long along the tube length. However, there is a multiplicity of these fin sections arranged serially on each tube.

It is important to leave spaces or slots between adjacent fin sections attached to a tube. These jSlOt-s 35 (Fig. 1) are relatively narrow, say from 1; to A" wide, preferably wide. Wider slots may be used but are wasteful of exchanger metal and volume. Similarly, spaces or slots (not shown) are left between adjacent fin sections within the tube. The multiple-section exterior and interior fins, interrupted by narrow slots 35 as above described, extend along the length of 4 each tube between the bailles 36 which are at the ends of the intermediate portion 23 and adjacent ports 24, the portion of the tubes disposed opposite the ports 24 and the portion of the oxygen tubes extending through headers l8 have no fins thereon.

With the construction hereinabove described, turbulent gas flow takes place through the chan- The use of a pair of Strips f lded accordion- 2;" nels formed by both the interior and the exterior fins on the tubes. Inother words, the spaces or slots 35 occurring at intervals of every 4 to 12" induce turbulence in the gas streams which would otherwise have a streamlined or transitional flow. The distance (4 to 12") between the slots 35 is such that at about the point where the turbulence induced by one slot disappears, there is another slot to make the stream turbulent again.

The tubes having the exterior fins, as hereinabove described, are assembled in a typical bundle, as shown in Fig. 2, the bundle being disposed within shell l0. The tubes are preferably arranged in the bundle so that oxygen does not flow through adjacent tubes.- The inner tubes of the bundle, it will be noted, have the fin sides defining the hexagonal outline in contact with the fin sides defining the hexagonal outline of contiguous tubes, so that there is metal-to-metal contact throughout substantially the full area of the hexa'gonal outline of the fins surrounding these inner tubes. The outer tubes of the bundle, as shown in Fig. 3, are nested relative to the inner tubes so that at least three fin sides defining the hexagonal outline are in contact with the fin sides of contiguous tubes, leaving, in the case of some of the outer tubes, three sides, and in the case of others, two sides of the hexagonal outline, not in contact with the hexagonal outline of other contiguous tubes. of the bundle of tubes and the interior of the shell I!) at intervals along the length of the shell is blanked-off b bailie plates 36, 36', etc. which prevent flow throughthis space and insure that flow of gas through the intermediate portion 23 of shell i0 takes place through the channels defined by the exterior fins 34 onthe tubes 21 and 32. The battle plates 36, 36', etc. also act as reinforcing stays, aligning the tube bundle within the shell Ill. The spaces between baiile plates are The space between the exterior.

filled with packing 31, e. g., crumpled aluminum foil or wood blocks. It is obvious that the shell can be made close-fitting relative to the tube bundle and that baflies and packing can thereby be eliminated. I

In operation, fiow of oxygen takes place through one port I2 into header l1, thence through the oxygen tubes 21 into the header ll, at the other end of the shell l0, the oxygen-leaving through the other port I2. This flow is continu- 32 into the header [8 at the other end of the shell M and exits through the port l9 associated therewith. At the same time, air enters at the end of the shell at which oxygen and nitrogen are leaving, through port 24 associated with the intermediate portion 23, flows through the channels defined by the exterior fins 34 surrounding both the oxygen tubes. 21 and the tubes 32 and exits through port 24 associated with-the other end of the intermediate portion 23. The air, therefore, flows counter-currently to both the nitrogen and the oxygen streams. Upon reversal, (indicated by dotted arrows in Fig. 1), air fiows through the adjacent port [9 into the header I8,

then through the tubes 32, exiting through the header l8 and port l9 associated therewith at the other end of the shell. During this reversal period, nitrogen flows through port 24 adjacent the port I9 through which air is exiting, then through the channels formed by exterior fins 34 in the intermediate portion 23 of the shell and exits through port 24 associated with the other end of the intermediate portion 23. As in the previous cycle of the operation, air flows countercurrently to both the nitrogen and oxygen streams.

It will be noted the cold exchanger has an exceptionally high surface area of cold exchanger surface per unit of volume of exchanger space.

having a wall thickness'of .035 to .083", preferably .065", the exchanger may have from 300 to 500 square feet of cold exchanger surface per cubic foot of exchanger volume. The flat surface contact between portions of the exterior and interior fins on the walls of the tubes results in high fin efficiency. The turbulent flow, caused by the spaced slots in the longitudinally extending channels, further improves the cold transfer efliciency.

of the exchanger. The exchanger is, therefore, of

exceptionally high cold transfer efficiency. This makes it possible to have the volumetric space through which nitrogen on the one hand and air on the other flows relatively small, thereby minimizing reversal losses. Because of the expansion joint l3 in the shell and expansion bellows 3'! in ,7 the oxygen tubes 21, notwithstanding the difiertubes takes place in a general longitudinal direction; hence, minimum pressure drop of fluid fiowing therethrough occurs.

8 The cold exchanger has been shown in Fig. l in a vertica1 position with the products of air rectification enterin at the lower end'thereof. If desired, air could instead be introduced at the lower end of the exchanger and the products of rectification introduced at the upper end. Furthermore, particularly in the case of large exchangers, it is advisable to support the cold exchanger in a horizontal position. There is also advantage in making the ports and associated headers at the warmer end of the exchanger larger than the corresponding parts at the colder end to compensate the volume changes occurring in the gaseous fluids flowing therethrough.

Different embodiments of the invention could be made without departing from the scope of this invention. For example, when the cold exchanger is made entirely from a single metal, the expansion joint I 3 and expansion bellows 3| may be omitted because there will be substantially no differential expansion and contraction between the shell and the tubes of the exchanger. Also, in some operations, the exchanger may be employed without reversal of fluid streams. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A heat exchanger comprising a, cylindrical shell, a pair of header plates in spaced relation at each end of the shell extending thereacross defining two contiguous headers at each end of the shell, the end headers being for flow of oxygen therethrough, and the adjacent headers and the intermediate portion of the shell serving for alternate flow therethrough of air and nitrogen,-

two sets of tubes, one set of tubes for fiow of oxygen therethrough connecting the end head-' ers and the other set of tubes connecting the said adjacent headers, each tube of both sets of tubes having an interior accordion fin of foil-like metal of high heat conductivity arranged to form four series of substantially triangular-shaped channels extending longitudinally through the tube, the base portions of two series of the triangular-shaped channels being in intimate contact with the interior surface of the tube and the base portions of the other two series of channels being in contact with each other and disposed in a plane bisecting the tube longitudinally, and an accordion fin on the exterior of the tube arranged to form two series of triangularshaped channels in contiguous relationship, with the base portions of the triangles of one series in intimate contact with the exterior surface of the tube and the base portions of the triangles of the other series spaced from the walls of said tube and arranged in a hexagonal outline surrounding the tube, said tubes being stacked within the shell to form a bundle of tubes, the inner tubes of said bundle having each Side of the hexagonal outline of exterior fins in contact throughout substantially the full area thereof with the side of the hexagonal outline of a contiguous tube in the bundle, andthe outer tubes in said bundle having at least three sides of said hexagonal outlines in contact with the sides of the hexagonal outlines of'the exterior fins on contiguous tubes, the remaining sides of each of said hexagonal outlines surrounding said outer tubes being disposed opposite the interior surface of the shell, bailies disposed at spaced intervals along the length of the shell in the space between the interior surface of the shell and the said remaining sides of said hexagonal outlines on the outer tubes of said bundle, whereby fiow of air takes place through the triangular channels defined by the said exterior fins, while at the same time flow ofnitrogen takes place" through the said adjacent headers and the interior of the second set of tubes, and upon reversal fiow of air takes place through said adjacent headers and through the interior of the second set of tubes and flow of nitrogen takes place through the said triangular channels defined by the said exterior fins, the now of oxygen taking place at all times through the end headers and the first-mentioned set of tubes, each set of fins on both the interior and exterior of each tube having at spaced pointsalong the length thereof relatively narrow slots so that turbulent flow of oxygen, nitrogen and air takes place, the tubes and fins being of copper while the shell 'is of nickel steel, an expansion joint substantially midway between the ends of the shell and expansion joints in each oxygen tube in the portions thereof extending through said adjacent headers.

2. A heat exchanger comprising a shell, a pair of header plates in spaced relation at each end of the shell extending thereacross defining two contiguous headers at each end of the shell, the end headers being for flow of oiwgen therethrough, and the adjacent headers and the intermediate portion of the shell serving for alternate fiow therethrough of air and nitrogen, two sets of tubes, one set of tubes for flow of oxygen therethrough connecting the end headers and the other set of tubes connecting the said adjacent headers, each tube of both sets of tubes having an interior accordion fin of foil-like metal of high heat conductivity arranged to form a multiplicity of channels extending longitudinal- 1y through the tube, the channels having portions in intimate contact with the interior surface of the tube, and an accordion fin on the exterior of each tube arranged to form a multiplicity of channels extending. longitudinally of the tube, said channels having base portions in intimate contact with the exterior surface of the tube and having the portions thereof remote from the walls of the tube, arranged in a polygonal outline surrounding the tube, said tubes being stacked within the shell to form a bundle of tubes with the polygonal outlines of the exterior fins on the inner tubes of the bundle in contact with the polygonal outlines of the fins on contiguous tubes, the space within the shell between the polygonal outlines of the exterior fins on the outer'tubes of the bundle and the 'interior surface of the shell being blocked off to prevent flow of fluid therethrough, the fins on both the exterior and interior of each tube havin at spaced points along the length thereof relatively narrow slots so that turbulent flow of fluid takes place through the interior of the tube and through the channels defined by the exterior fins, the tubes and fins being of high heat conducting material while the shell is of a material having a difi'erent coeificient of expansion than that of the tubes, an expansion joint substantially midway between the ends of the shell and expansion joints in each of the first-mentioned set of tubes in the portions thereof extending through said adjacent headers.

3. A heat exchanger comprising a shell, a, pair of header plates in spaced relation'at eachend of the shell extending thereacross defining two contiguous headers at each end of the shell, two sets of tubes, one set of tubes connecting the of tubes having an interior accordion fin of foillike metal of high heat conductivity arranged to form four series of substantially triangularshaped channels extending longitudinally through the tube, the base portions of two series of the triangular-shaped channels being in intimate contact with the interior surface of the tube and the base portions of the other two series of channels being in contact with each other and disposed in a plane bisecting the tube longitudinally. and an accordion fin on the exterior of the tube arranged to form two series of triangular-shaped channels in contiguous relationship, with the base portions of the triangles of one series in intimate contact with the exterior surface of the tube and the base portions of the triangles of the other series spaced from the walls of said tube and arranged in a hexagonal outline surrounding the tube, said tubes being stacked within the shell to form a bundle of tubes, the-inner tubes in said bundle having each side of the hexagonal outline of exterior fins in contact throughout substantially the full area thereof with the side of the hexagonal outline of a contiguous tube in a bundle, and the outertubes in said bundle having at least three sides of said hexagonal outlines, in contact respectively with the sides of the hexagonal outlines of contiguous tubes, the remaining sides of each of the hexagonal outlines surrounding said outer tubes being disposed opposite the interior surface of the shell, and baflles disposed at spaced intervals along the length of the shell in the space between the interior surface of the shell and the said remaining sides of the hexagonal outlines on the outer tubes of said bundle.

- 4. A heat exchanger comprising a shell, a pair of header plates in spaced relation at each end of the shell extending thereacross defining two contiguous headers at each end of the shell, two sets of tubes, one set of tubes connecting the end headers and the other set of tubes connecting the adjacent headers, each tube of both sets of tubes having an interior accordion fin of foil-like metal of high heat conductivity arranged to form four series of substantially triangular-shaped channels extending longitudinally through the tube, the base portions of two series of the triangularshaped chamiels being in intimate contact with the interior surface of the tube and the base portions of the other two series of channels being in contact with each other and disposed in a plane bisecting the tube longitudinally, and an accordion fin on the exterior of the tube arranged to form two series of triangular-shaped channels in contiguous relationship, with the base portions of the triangles of one series in intimate contact with the exterior surface of the tube and the base portions of the triangles of the other series spaced from the walls of said tube and arranged in a hexagonal outline surrounding the tube, said tubes being stacked within the shell to form a bundle of tubes, the inner tubes in said bundle having each side of the hexagonal outline of exterior fins in contact throughout substantially the full area thereof with the side of the hexagonal outline of a contiguous tube in the bundle, and the outer tubes in said bundle having at least three sides of said hexagonal outlines in contact respectively with the sides of the hexagonal outlines of contiguous tubes, the remaining sides of each of the hexagonal outlines surrounding said outer tubes in said bundle being disposedopposite the interior surface of the shell.

5. A heat exchanger comprising a shell, a plurality of tubes in said shell, each tube having an interioraccordion fin of foil-like metal of high heat conductivity arranged to form four series of substantially triangular-shaped channels extending longitudinally through the tube, the base portions of two series of the triangular-shaped channels being in intimate contact with the interior surface of the tube and the base portions of the other two series of channels beingjncontact with each other and disposed in a plane bisecting the I tube longitudinally, and an accordion fin on the exterior of the tube arranged to form two series of triangular-shaped channels in contiguous relationship, with the base portions of the triangles of one series in intimate contact with the exterior surface of the tube and the base portions of the triangles of the other series spaced from the walls of said tube and arranged in a hexagonal outline surrounding the tube, said tubes being stacked within the shell to form a bundle of tubes, the inner tubes in said bundle having each side of the hexagonal outline of exterior fins in contact throughout substantially the full area thereof with the side of the hexagonal outline of a contiguous tube in the bundle, and the outer tubes in said bundle having at least three ,sides of said hexagonal outlines in contact respectively with the sides 'of the hexagonal outlines of contiguous tubes, the remaining sides of each of the hexagonal outlines surrounding said outer tubes being disposed opposite the interior surface of the shell; r

6. A heat-exchanger comprising a cylindrical shell, two spaced header plates at each of the opposite ends of the shell defining a first and second header at each end'of the shell, the said first headers being contiguous to the ends of the shell and the portion of the shell between the said second headers constituting the intermediate portion of said shell, two sets of tubes each provided shell of nickel steel, two spaced header plates at each of the opposite ends of the shell defining a first and second header at eachend of the shell the said first headers being contiguous to the ends of the shell and the portions of the shell between the said second headers constituting the intermediate portion of said saw, two sets of copper tubes each provided with exterior and interior copper fins, one set, containing a smaller number of tubes than in the other set, extending from the said first header at one end of the shell to said first header at the other end of the shell to place said first headers in communication with each other through said first mentioned set of tubes and the other set extending from the said second header at one end of the shell to the said second header at the other end of the shell to place said second headers in communication with each other said intermediate portion of the shell and all of said tubes and expansion joints in each of the first mentioned set of tubes disposed in the opposite end portions thereof passing through said second headers to take care of differential expansion between ,the end portions of the shell and the first mentioned set of tubes.

8. A heat exchanger tube having an interior accordion fin of foil-like metal of high heat con communication with each other through said 1 second set of tubes, said two sets of tubes being arranged with the exterior surfaces of the tubes of one set facing the exterior surfaces of the tubes of the other set and the first mentioned set,

of tubes having the opposite end portions of each 'tube afilxed to both of said two spaced header plates at each of the opposite ends of said shell, the tubes being of high heat conducting material, the shell being made of a different material having a different coefficient of expansion than that of the tubes, an expansion joint in the said intermediate portion of the shell to take care of difductivity arranged to form four series of substantially triangular-shaped channels extending longitudinally through the tube, the base portions of two series of the triangular-shaped channels being in intimate contact with the interior surface of the tube and the base portions of the other two series of channels being in contact with each other and disposed in a plane bisecting the tube longitudinally.

9. A multi-tube heat exchanger comprising a shell and a plurality of tubes, each tube having an interior accordion fin of foil-like metal of high heat conductivity arranged to form four series of substantially triangular-shaped channels extending longitudinally through the tube, the base portions of two series of the. triangular-shaped channels being in intimate contact with the interior surface of the tube and the base portions of the other two series of channels being in contact with each other and disposed in a plane bisecting the tube longitudinally, and an accordion ferential expansion between the said intermediate take care of differential expansion betweenthe end portions of the shell and the first mentioned set of tubes. 7. A heat exchanger comprising a cylindrical fin on theexterior of each tube arranged to form two series of triangular shaped channels in contiguous relationship with the base portions of the triangles of one series in intimate contact with the exterior surface of the tube and the base portions of the triangles of the other series spaced from the wallsof said tube and arranged in hexagonal outline surrounding the tube, said tubes being stacked within the shell to form a bundle of tubes with the inner tubes -of said bundle having the sides of said hexagonal outline in contact with each other, the outer ,tubes in said bundle having at least three sides of said hexagonal outline incontact with the sides of the hexagonal outlines of the exterior fins on contiguous tubes and the remaining sides of each of said hexagonal outlines surrounding said outer 13 tubes being disposed opposite the interior surfac Number of the shell. 2,075,511 EDWARD G. SCHEIBEL. 2,198,555 2,382,255 REFERENCES CITED 5 v The following references are of record in the file of this patent: z gi s l UNITED STATES PATENTS of 902 Number Name Date 1'. 371,608 153,776 Mason Aug. 4, 1874 516,065 164,757 North June 22, 1875 44,339 1,920,800 McCausland Aug. 1, 1933 Name Date De Baufre Mar. 30, 1937 Wilson et a1 Apr. 23, 1940 Pyzel Aug. 14, 1945 FOREIGN PATENTS Country Date Great Britain Nov. 26, 1903 Great Britain Apr. 28, 1932 France Apr. 13, 1921 v Switzerland May 3, 1908 

